Recently, a focus has been placed on a touch detection device, a so-called touch panel, which is capable of detecting an external proximity object. The touch panel is provided as a display device with a touch detection function in the state of being equipped on a display device, for example, on a liquid crystal display device, or being integrated with the liquid crystal display device.
There is provided a touch panel capable of using a pen as the external proximity object. For example, it is possible to designate a small area or input a handwritten letter by allowing the pen to be used. There are various types of techniques to detect touch by the pen. One of the various types of techniques is an electromagnetic induction system. This electromagnetic induction system can realize a high accuracy and a high writing pressure detection accuracy, and also can realize a hovering detection function in which the external proximity object is spaced apart from a touch panel surface, and thus, this is effective as a technique of detecting the touch by the pen.
Touch detection techniques using the electromagnetic induction system are described in, for example, Japanese Patent Application Laid-Open Publication No. H10 (1998)-49301 (Patent Document 1), No. 2005-352572 (Patent Document 2), and No. 2006-163745 (Patent Document 3).
Further, there is provided a touch detection device capable of detecting a finger or the like as the external proximity object. In this case, a detection target is different from the pen, and thus, another system, different from the electromagnetic induction system, is employed as a technique of detecting a touch. For example, there are systems that detect an optical change, a change of a resistance value, or a change of an electric field caused by touch of a finger or the like. For example, there is a capacitive system using a capacitance, as the system that detects the change of the electric field among these systems. This capacitive system has a relatively simple structure, and consumes low power, and thus, has been used in a portable information terminal or the like.